B-waves in noninvasive capacitance signal correlate with B-waves in ICP.

Abstract

Analysis of B-waves in overnight intracranial pressure (ICP) recordings used to be an important element in the diagnosis of normal pressure hydrocephalus (NPH). Here, we tested the hypothesis that equivalents to B-waves can be detected and quantified in a noninvasively measured electric capacitance signal termed W. We measured ICP and W in a cohort of 15 patients with suspected diagnosis of NPH or spontaneous intracranial hypotension during infusion testing, identifying B-waves in both signals by wave-template matching in the time domain. We found very strong correlation between the duration of B-waves in ICP and W (R² = 0.86, p < 10^-6), and weak correlation between the average B-wave amplitudes in ICP and W (R = 0.34, p = 0.02). The concurrent presence of B-waves in the signals suggests that vasogenic activity of cerebral autoregulation is reflected in W. The weaker correlation of amplitudes may be attributed to W being an indirect measure of cranial volume composition, whereas ICP is a measure of pressure, with the two linked by the non-linear craniospinal pressure-volume relation that varies between patients. Analysis of the noninvasively acquired W signal should be evaluated as a triage tool for patients with NPH and other disorders characterized by reduced compliance.